The field of the present invention is separators employing screens.
Screen systems have long been employed to separate solids from liquids and solids of different sizes by passage over and through wire mesh screens. The screens can be rectangular or circular. Typically, the screens are drawn taunt, positioned horizontally, and a material to be separated is propelled at the screen. One component of the material passes through the screen, and a second component of the material floats over the screen to a discharge point. Often, the screen is vibrated to increase the separation rate.
Efforts to increase the separation rate, encounter increased difficulties with screen wear, impingement screen blinding, screen stretching, and screen fatigue. Impingement screen blinding occurs where the feed stream continuously hits the same spot on the screen. The flow then moves horizontally from the point of impact providing continuing inefficient screening which progessively gets worse as screen blinding increases. An effective blind area on the screen exists because a layer of flow, typically solids, constantly covers the screen, reducing the flow rate through and over the screen.
To a certain extent, screen wear, screen stretching, and screen fatigue are expected conditions, but they become special problems when localized. Excessive wear on one portion of the screen can result in early failure. For example, when a screen is fed centrally, wear, stretching, and fatigue become localized in the center of the screen; and the problem of impingement screen blinding tends to occur in the center of the screen. Material has also been fed across the entire surface of the screen, but the foregoing problems can still exist because the flow of material to the feed points on the screen is continuous. As the flow rate of the material is increased, these problems are intensified.